1. Field of the Invention
The present invention relates to an optical apparatus for combining light modulated by a reflection type liquid crystal display device and to a projection apparatus using the same.
2. Description of the Related Art
Known in the art is a projection type display device for displaying projected image by spatially modulating and emitting incident light and focusing and projecting the emitted light according to an electric signal supplied to a spatial light modulation device. In general, a color display projection apparatus has an illumination optical system having a light source constituted by a lamp and a condensing mirror, splitting the light emitted from the light source to three wavelength bands, and condensing the split lights at corresponding spatial light modulation devices to illuminate, a light combining prism for combining lights modulated by spatial light modulation devices, and a projection lens for projecting the emitted light of the light combining prism to a screen etc. (the projection apparatus will be referred to as a “projector” hereinafter).
A liquid crystal projector uses spatial light modulation devices using liquid crystal materials (hereinafter, referred to as “liquid crystal panels”). As the projector, a transmission type projector passing light through the liquid crystal panels and modulating the light in the process of passing through the liquid crystal panels and a reflection type projector emitting light to the liquid crystal panels and modulating the light when reflected at the liquid crystal panels to change the polarization axes are known.
A reflection type liquid crystal projector using reflection type liquid crystal panels can be realized with small sized panels with a high resolution. A reflection type liquid crystal projector requires use of a polarization element able to combine and split two perpendicular linear polarized beams (s polarized light and p polarized light).
As such a polarization element, a polarized beam splitter constituted by a glass block is known (refer to Japanese Unexamined Patent Publication (Kokai) No. 2001-350024). As disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2001-350024, by forming a plurality of thin films between two pieces of glass, it becomes possible to split or combined two linear polarized beams.
However, such a polarized beam splitter constituted by a glass material is affected in characteristics by distortion of the glass, therefore low distortion glass must be used. For this, lead etc. must be dissolved in the glass resulting in glass having a very high specific gravity. There therefore arises the problem of increase of the weight.
As opposed to this, as a projector realizing a light weight reflection type liquid crystal panel optical system, a projector using a reflection type polarization plate has been proposed (refer to Japanese Unexamined Patent Publication (Kokai) No. 2003-508813). Japanese Unexamined Patent Publication (Kokai) No. 2003-508813 proposes a projector using a wire grid element forming a metal conductor in a lattice state to split incident light into two perpendicular linear polarized beams one of which passes through the plate and the other of which is reflected at the plate. In an optical system using such a reflection type polarization plate, a reduction of weight can be realized.
When using three reflection type liquid crystal panels, inputting the three primary colors of light to the panels, combining the modulated light again, a projector enabling full color display can be realized.
FIG. 1 is a view of the schematic configuration of an optical system of a liquid crystal projector using three liquid crystal panels and able to display not a black and white, but a color image.
This liquid crystal projector 10 has, as shown in FIG. 1, a light source 11 having a lamp 111 and a condensing mirror 112, an illumination optical system 12, three reflection type liquid crystal panels 13R, 13G, and 13B, a light combining prism 14, and a projection lens 15.
The illumination optical system 12 has a lens 121 oriented so that light output from the optical system having the function of aligning the light emitted from the light source 11 with a predetermined polarization (for example p polarization) is emitted toward the reflection type liquid crystal panels 13R, 13G, and 13B, a dichroic mirror 122 for splitting it into light LR having a red wavelength region and light LGB having green and blue wavelength regions, a reflection mirror 123 for reflecting the red light LR split at the dichroic mirror 122, a reflection mirror 124 for reflecting the green and blue light LGB split at the dichroic mirror 122, a dichroic mirror 125 for reflecting only the green wavelength region in the light LGB reflected at the reflection mirror 124 and passing the blue wavelength region therethrough, a polarization plate 126R for passing the p polarized red light LR reflected at the reflection mirror 123 therethrough to make it strike the reflection type liquid crystal panel 13R and reflecting the red light spatially modulated and s polarized at the reflection type liquid crystal panel 13R and making it strike the light combining prism 14, a polarization plate 126G for passing the p polarized green light LG reflected at the dichroic mirror 125 therethrough to make it strike the reflection type liquid crystal panel 13G and reflecting the green light spatially modulated and s polarized at the reflection type liquid crystal panel 13G and making it strike the light combining prism 14, a polarization plate 126B for passing the p polarized blue light LB reflected at the dichroic mirror 125 therethrough to make it strike the reflection type liquid crystal panel 13B and reflecting the blue light spatially modulated and s polarized at the reflection type liquid crystal panel 13B and making it strike the light combining prism 14, and optical lenses 127 to 129 arranged at incident sides of the polarization plates 126R, 126G, and 126B.
In the liquid crystal projector 10, white light output from the light source 11 is made uniform by a not shown integrating optical system (integrator) and aligned with a predetermined polarization by a polarization conversion element (P-S converter). Then, the output light is oriented by the lens 121 of the illumination optical system 11 so as to strike the reflection type liquid crystal panels 13R, 13G, and 13B and then split to three wavelength regions of light by the color splitting mirrors constituted by the dichroic mirrors 122, 125, etc. The split color beams of light strike the reflection type polarization plates. Only the light in a certain polarization direction is selected by the polarization plates 126R, 126G, and 126B and strikes the reflection type liquid crystal panels 13R, 13G, and 13B. The reflection type liquid crystal panels 13R, 13G, and 13B are struck by RGB light.
Video signals (image signals) of colors corresponding to the incident light are supplied to the reflection type liquid crystal panels 13R, 13G, and 13B, whereupon the incident light beams are rotated in polarization directions, modulated, and output according to the video signals. The modulated light beams emitted from the liquid crystal panels strike the polarization plates 126R, 126G, and 126B again. Only the polarized light component rotated by 90 degrees is selected from among the polarized beams of light striking the polarization plates 126R, 126G, and 126B and striking the light combining prism 14. The color beams of light modulated at the three reflection type liquid crystal panels are combined and emitted to the same direction at the light combining prism 14. The emitted combined light from the light combining prism 14 is output and projected to a screen etc. by the projection lens 15.